On Fri, Oct 12, 2001 at 08:33:15PM +0900, Dylan Thurston wrote: > So when I read the "Syntactic Sugar for Arrows" proposal, my initial > reaction is "Wow, that's a little complicated. It doesn't look like > syntactic sugar to me."
Why, thank you! > This contrasts with the do-notation, which does look like syntactic > sugar: you can rewrite any do expression in terms of the basic > combinators with a bounded amount of pain.[1] Somehow with Arrows > the point-free syntax you are forced into is extraordinarily unwieldy, > and the arrows "syntactic sugar" is much handier. I guess it's the generality of the arrows interface that makes it so awkward to use. There are some examples of this awkwardness in sections 7 and (especially) 9 of the draft version of John Hughes's arrows paper (http://www.cs.chalmers.se/~rjmh/arrows.ps or .pdf). > Incidentally, it seems to me that this is one case where a Lisp-like > macro facility might be useful. With Haskell, it is impossible to > play with bindings, while presumably you can do this with good Lisp > macro systems. If you extend the syntax using macros, it's essential for pain-limitation that errors are presented in terms of derived type rules for the macros. There's a paper on type-safe macros (not Haskell, but could be) in ICFP 2001 by Ganz, Sabry and Taha. The arrows stuff seems like it would require a second-order variant though (macros with macro arguments). _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
